The invention relates to a jointless artificial foot for a leg prosthesis. The invention especially relates to such a jointless artificial foot having a resilient foot insert which is arranged inside a foot molding, is of approximately C-shaped design in longitudinal section, with the opening to the rear, and takes up the prosthesis load with its upper C-limb and via its lower C-limb transmits that load to a leaf spring connected thereto, which spring extends, approximately parallel to the sole region, forward beyond the foot insert and the front end of which projects right into the foot-tip region.
Initial proposed solutions envisaged the artificial foot having a rigid construction made, for example, of wood, which was subsequently provided with a joint, in order to imitate the function of the ankle. Then, in a further development, a resilient foot insert which was composed of leaf springs and was coated with foam was envisaged (cf. e.g. U.S. Pat. No. 4,959,073).
DE 40 38 063 C2 discloses a jointless prosthesis foot having a foot insert which is of one-piece design, permits at least a plantar and dorsal flexion and an axial compression and, in the longitudinal section of the foot, has an approximately S-shaped design. The upper limb, together with a front oblique limb adjoining at an obtuse angle, forms an angular element, which is rigid overall and the lower end of which is adjoined by a central, leaf spring-like limb which, at its rear end, is connected to the lower limb via an approximately semi-circular limb connection. In this case, the lower end of the rigid angle element extends forward approximately into the region of the tough basic joints.
FR-A1-26 40 499 discloses a jointless artificial foot in which the central part of the approximately C-shaped foot insert lies roughly in the front third of the length of the sole, while the upper C-limb forms a connection to the leg prosthesis. The C-shaped foot insert assumes a spring function which is supplemented by a resilient cushion placed between the two C-limbs, in order to achieve a certain suppleness when putting the foot on the ground. However, it has been shown in practice that even this artificial foot does not permit a natural walking motion.
Furthermore, German Utility Model G 93 15 665.0 discloses a comparable jointless artificial foot. This document provides a foamed plastic foot molding having a metallic reinforcement element which is formed by a U-shaped profile, the respective limbs of which can be moved elastically toward one another under load. The terminating limb ends have a decreasing material thickness toward their free end, while the limb ends are provided with thickened portions. The lower U-limb is screwed to a leaf spring at its free end, while the upper U-limb is connected to the holder of a leg connection part. The leaf spring may consist of carbon fiber or titanium. The space between the free U-limbs may be filled with a soft polyurethane foam. This elastic spring element is intended to permit a foot movement in the manner of a pro/supination about the longitudinal axis of the foot and a natural movement sequence.